This disclosure relates to the imaging of particles with diameters smaller than a few millimeters down to a few microns in dry or liquid samples using a microscope equipped with a digital video camera. The method of detection is bright field microscopy (the direction of observation is perpendicular to the illuminated background surface). The instrument to perform such an analysis comprises a cell (translucent tunnel) with particles falling or flowing inside it. Those particles are illuminated by a defocused (flat) light source present in the background and a video recording of light passing between particles (obfuscation); see e.g. U.S. Pat. Nos. 4,338,024; 5,296,910; and 5,359,907, all of which are incorporated herein by reference.
Different sizes and shapes of particles can be visualized and analyzed by dark images of particle silhouettes on the bright background. Typically, such instruments use only one video camera, with sophisticated models having two cameras but with parallel or nearly parallel axes (observing particles from the same direction but with different enlargement or observing transmitted and scattered light); see e.g. U.S. Pat. Nos. 6,061,130; 7,907,279; 8,681,215; 9,897,525; and 10,184,875, all of which are incorporated herein by reference.
The limitations of computer bandwidth and processing power has prevented, until recently, practical designs of instruments with more cameras observing particles from different, perpendicular directions that would make for better characterization of particles' shapes and ultimately better estimate their volume, which is of interest for many research and production facilities. Modern cameras and networking technology allow for multi-camera recording with high resolution.
With several cameras employed, however, it is very difficult to align all optical systems so that these devices record images for exactly same points or volumes of a sample in space. Therefore, a system and method for calibrating a multi-sensor system is needed.